Some conventional image sensing apparatuses can internally change color conversion parameters (hue levels, saturation levels, gamma tables, contrast levels, and the like) to obtain an image of user's preference. In general, in such image sensing apparatus, the user can select a desired one of a plurality of parameter sets prepared in advance by a manufacturer, and a color conversion process is executed using the selected parameter set to obtain an image of user's preference (see Japanese Patent Laid-Open No. 11-187351).
However, in such conventional image sensing apparatus, upon setting the color conversion parameters, the user must actually change color conversion parameters to sense a similar scene, and must confirm if an image of his or her preference is obtained. That is, the setups of the color conversion parameters force such trial-and-error sequences, resulting in very complicated operations.
Such change process of the color conversion parameters in the conventional image sensing apparatus suffers the following problems: the degree of freedom in change is small, and the need for changing only a specific color (e.g., a color of sky) cannot be met since such change influences all colors to be reproduced. For this reason, a setup that the user wants cannot always be attained, and it becomes difficult to obtain an image of user's preference.
As a method of performing color conversion to change the color of an image captured using a digital camera or scanner to a preferred color appearance, a method of generating a color conversion table (lookup table) and performing color conversion using that table has been proposed. For example, a color expressed on a three-dimensional (3D) color space such as an RGB color space or the like can undergo color conversion by preparing a 3D lookup table. Color conversion using such lookup table allows to freely design color conversion parameters, e.g., to convert only a local color on the color space.
However, a local color can be changed, but then the continuity of table data may be lost when parameters which change a color extremely are set. For example, when certain data in a lookup table is set to change an input color extremely, surrounding input colors change largely. For this reason, the output colors become unnatural.
Under such circumstances of the prior arts, an image processing technique that allows to easily obtain an image of user's preference is demanded.
For example, it is demanded to automatically set color conversion parameters on the basis of images before and after an edit process by retouching or the like, and to easily realize color conversion of user's preference.
Also, it is demanded to automatically set color conversion parameters from a pair of colors designated by the user, and to easily realize color conversion of user's preference.
Furthermore, a technique that can change only a desired color and colors close to that color is demanded.
Moreover, it is demanded to prevent discontinuity of colors in a reproduced image in a color conversion technique using a color conversion table.